[Pw_forum] problem in vc-relax

[Ashish Kumar]

Hello to all,

I have tried for the vc-relax of Mo2C hexagonal system, job is not done
properly it come out in between and the atomic positions

what I have given in the input file and what I am getting in the out file is
different.
(i) Why the crystal positions changes. what I think that the nature of the
atomic postions must be retained.

In Input file
ATOMIC_POSITIONS (alat)
C        0.00  0.00 0.00
Mo       0.3333333   0.666666   0.25
Mo       0.6666666   0.333333   0.75



In out file we get

CELL_PARAMETERS (alat=  5.67296009)
   0.946518633   0.001215132  -0.004855406
  -0.474470641   0.819090796  -0.000958606
   0.009278926   0.007480907   1.741942673

ATOMIC_POSITIONS (alat)
C        0.156590059   0.041446237  -0.212516996
Mo       0.157761886   0.589915381   0.269109338
Mo       0.636664528   0.321113609   1.041609035




(ii) why cell_parameter changes in the out file . (I think that for
hexagonal system it must be what given in the input file)


my input file

&control
    calculation='vc-relax'
    restart_mode='from_scratch',
    pseudo_dir = '/home/ashish/softwares/espresso/pseudo/',
    outdir='/home/ashish/dft/espresso_mo2c/test1/tmp_espresso/'
    prefix='mo2c'
    tprnfor = .true.,
    tstress = .true.
 /
 &system
    ibrav=4, celldm(1) =5.672960087 , celldm(3)=1.573617588 , nat=3, ntyp=2,
    nspin = 1,  starting_magnetization(1)=0.7,
    ecutwfc = 24.0, ecutrho = 288.0,
    occupations='smearing', smearing='methfessel-paxton', degauss=0.02
 /
 &electrons
    diagonalization='cg'
    conv_thr = 1.0e-8
    mixing_beta = 0.7
/
&ions
  ion_dynamics='bfgs'
 /
&cell
cell_dynamics='bfgs'
/
ATOMIC_SPECIES {crystal}
 C  12.01 C.pw91-van_ak.UPF
 Mo 95.94 Mo.pw91-n-van.UPF
ATOMIC_POSITIONS
 C 0.0 0.0 0.0
 Mo 1/3 2/3 1/4
 Mo 2/3 1/3 3/4

K_POINTS automatic
 4 4 4   0 0 0


 can any one help me. What is the mistake (in my input file or else)


with best wishes
Ashish
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